Termination by employer under absconding

I was working with a company for more than 4.5 years and even worked in second shift till 10 pm in night for about 3.5 years I had a good performance record in all the annual performance reviews.I had some health issues and was on leave this was informed to my manager and HR.After I joined back my company asked me to work in 8 AM shift which I did not feel feasible as I had just recovered, HR asked for medical certificate saying I am not able to work in 8 Am shift my employment letter does not have any clause saying I will work in any shift still they blamed me for not being flexible and said this is my last chance. I again felt not well and went on leave this time did not drop mail about my sickness within one week HR sent a mail saying respond today and before I couldsee the mail on next working day itself dropped another mail saying we have initiated termination and in few days I got termination with no show cause letter received and now after 3 months company asking for notice period recovery I did not resign I was terminated without any notice and still they are asking me for notice period amount and they have not even given my experience or relieving letters which is making it difficult for me to get another job Can. Anyone please advice what i should do in this case